User control interface for laser simulating sandblasting apparatus

ABSTRACT

A laser system for processing surfaces of a variety of materials. The amount of laser treatment received by a surface and the geometry are controlled by an impact frequency matrix that is programmed into a control computer. The control computer can control a scanning laser beam to simulate the statistically random property of the particle distribution in a sandblasting process to generate a feathered worn look.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of the U.S. patentapplication Ser. No. 08/839,165, filed on Apr. 21, 1997, the disclosureof which is incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to a surface treatment with a laser, and morespecifically, to a system and method for processing surfaces made of avariety of materials with at least one laser beam.

BACKGROUND OF THE INVENTION

A laser beam can interact with a surface in a number of ways to changethe surface properties, including light absorption, photon scatteringand impact. For example, a surface may be burned by an intense laserbeam. Some surface particles may be ablated from a surface by the impactof a laser beam. Therefore, a surface can be treated with one or moreproper lasers to achieve certain effects that may not be easily donewith other methods.

One example is described in a copending U.S. patent application Ser. No.08/729,493, pending, titled "LASER METHOD OF SCRIBING GRAPHICS", whichis a continuation-in-part of the U.S. patent application Ser. No.08/550,339, filed on Oct. 30, 1995 by the present inventors. Thedisclosure of the application "LASER METHOD OF SCRIBING GRAPHICS" isincorporated herein by reference. This application describes the use oflasers to form graphics on various materials by controlling the energydensity per unit time. The graphics can be patterns, images, letters,and or any other visual marks.

Although other traditional methods, such as dyeing, printing, weaving,embossing and stamping, have been widely used, laser methods appear tohave certain advantages in producing complex and intricate graphics onthe materials. This is at least in part because many of the traditionalmethods lack the necessary registration and precision to insure thatminute details of the graphics are accurately and repeatably presentedon the materials. In addition, laser methods obviate many problemsassociated with the traditional methods such as high cost of equipmentmanufacturing, equipment maintenance, and operation, and environmentalproblems. A detailed description of laser methods for scribing graphicsis disclosed by the present inventors in the above-referenced U.S.Patent Application "LASER METHOD OF SCRIBING GRAPHICS".

The extent of laser interaction with a material can be characterized bya number of parameters, including spot size, intensity, power, etc. Theinventors found that one preferred parameter is the energy density perunit time ("EDPUT") defined as ##EQU1## wherein the projection speed isthe speed at which the scanning beam spot moves on a treated surface.The laser operational parameters, i.e., laser power, beam spot size, andthe scanning speed, should be adjusted to achieve an optimal EDPUT for aspecific material and a particular scribing requirement. If the EDPUT istoo high, the surface may be carbonized, burned or melted; if the EDPUTis too low, the effect of laser treatment may not be sufficientlyvisible.

The inventors recognized that lasers can also be used to treat amaterial surface in order to achieve a certain texture or appearance ofthe surface. Many materials used by the fabric industry are treated forthis purpose.

Denim fabrics may undergo a sandblasting process to obtain a worn look.Denim jeans are often sold with a worn look in the upper knee portionsand back seat portion. The effect is similar to a feathered or shadowedlook in which the degree of the worn look continuously changes along thelength and width of the seemingly "worn" areas.

A sandblast treatment conventionally abrades the jeans with sandparticles, metal particles or other materials at selected areas toimpart a worn look with a desired degree of wear. This process blastssand particles from a sandblasting device to a pair of jeans. The randomspatial distribution of the sand creates a unique appearance in atreated area. Denim jeans and other clothing treated with such asandblast process have been very popular in the consumer market.

However, the sandblast process has a number of problems and limitations.For example, the process of blasting sand or other abrasive particlespresents significant environmental issues. A worker usually needs towear protective gear and masks to reduce the impact of inhaling anyairborne sand or other abrasive particles that are used. The actualblasting process typically occurs in a room which is shielded from otherareas in a manufacturing facility. Further environmental issues arisewith the clean-up and disposal of the sand. In practice, undesired sandis rarely completely eliminated from the pockets of the denim jeans orjackets.

The sandblasting process is an abrasive process, which causes wear tothe sandblasting equipment. Typically, the actual equipment needs to bereplaced as often as after one year of normal operation. This can resultin added capital expense and installation.

In addition, the actual cost of the sandblasting process is estimated ashigh as several dollars per unit garment depending upon capacityutilization. This high cost is at least in part due to the laborinvolved, the cost of the equipment repair or continual purchase, theenvironmental clean-up required, the sand used, and actual yield of thegoods.

Furthermore, the sandblasting process can adversely affect the strengthand durability of the finished goods due to the abrasion of the sand orother particles that are used.

Despite the above problems and limitations, the sandblast process isstill in wide use simply because there is no other alternative techniquethat can economically produce the desired surface appearance of thesandblast treatment. In view of the above, the inventors found itdesirable to replace the sandblast process with a new environmentallyfriendly process which is capable of producing the "sandblast look",while reducing the cost and maintaining the durability of the finishedgoods.

In recognition of the above, the inventors invented laser scribingmethods to achieve the worn look on fabrics such as denim, the detailsof which are disclosed in the above incorporated U.S. Patent Application"LASER METHOD OF SCRIBING GRAPHICS". For example, one method is to drapethe denim over a cone, cup or wedge surface that is positioned relativeto a laser with a beam scanning device so that the focused beam projectsdifferent spot sizes at the different location of the surfaces due to adistance variation from the focusing distance. Thus, the beam intensitychanges with the beam location on the surface. Accordingly, the degreeof laser scribing or the EDPUT on a piece of fabric on the surfacechanges. The laser sweeps over the surface to scribe a predeterminedpattern such as a solid pattern or a pattern with closely spaced lines.The locations on the surface that are closest to the focusing distanceto the laser receive the highest beam intensity or EDPUT and hence havethe more worn appearance. Conversely, the locations on the surface thatare most out of the focusing distance experience the lowest beamintensity or EDPUT and hence have the least worn appearance. Thistechnique has the effect of continuously changing the laser focus as thelaser beam scribes a pattern on the material. Alternatively, the laserfocus can be changed with respect to a flat work surface to achieve thesame effect.

Another method previously disclosed by the inventors relies upon using areference EDPUT grid over a treated area. Again, a pattern is scribed inthe treated area on a material surface. However, the operatingparameters of the scanning laser are changed along the grid with apredetermined EDPUT distribution to achieve a desired effect, such as afeathered look.

A third method uses a pattern having a series of lines with continuouslyincreasing or decreasing line spacing and thickness to achieve thefeathered or worn look. Alternatively, a radial gradient pattern canalso be created by the scanning laser with predetermined EDPUTs toproduce a desired fabric appearance.

The results of the above laser scribing techniques produced a"feathered" look that approximates the worn look achieved from thesandblast process. However, the treated fabric does not exactlyreplicate the well-recognized worn appearance produced by the sandblastprocess. This is at least in part due to the fact that the laserscribing techniques are essentially based on scribing with a regularpattern rather than the spatially random hits of the blasted sand orother abrasive particles. Also, the above laser methods usually havelong processing cycle times. For example, a typical cycle time of 6minutes or more is needed to process an oval section of 21 inches inlength.

Another limitation is that laser scribing requires a certain patternwith certain laser operating parameters (e.g., EDPUT) for a particularfabric in order to create a worn look. Since this can change from onefabric to another, the methods are very material specific and are notuniversally applicable to different fabrics.

SUMMARY OF THE INVENTION

The present invention uses a laser surface-processing system to simulatethe worn look on a fabric surface produced by a sandblast process in aneconomic way.

This is accomplished, at least in part, by forming a random computersimulation of the appearance of a sandblasted fabric and using at leastone laser beam to mark the material in the shape of the sandblastedfabric.

According to one embodiment of the invention, the laser systemcomprises: a laser system that produces a laser beam of a predeterminedamount of output energy range which scans over a surface of a materialto mark a user-defined pattern thereon in response to an appliedcommand; a controller having a microprocessor and a memory unit andcommunicating with said laser system to generate said applied commandaccording to a respective laser impact frequency information indicativeof said user-defined pattern; and a user control interface having a userinput device and a display to produce a graphic representation of saiduser-defined pattern based on said laser impact frequency information.

One aspect of the invention is a capability of displaying the surfaceappearance prior to actual processing a surface with the laser.

Another aspect of the invention is user modification of the laser impactfrequency information prior to actual processing. This may be achievedby changing parameters of a pattern density matrix, a probabilitydensity matrix or a impact frequency matrix that determines the lasercontrol codes.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects and advantages of the present invention willbecome more apparent in light of the following detailed description, asillustrated in the accompanying drawings, in which:

FIG. 1 is a block diagram showing a laser processing system for treatinga surface of a workpiece in accordance with one embodiment of theinvention.

FIG. 2 shows an exemplary embodiment of the system of FIG. 1 with twogalvo mirrors for scanning the laser beam on a workpiece surface.

FIG. 3 is a flowchart showing one exemplary method in accordance withthe invention.

FIG. 4 shows an exemplary elliptical pattern with a worn look on agarment.

FIG. 5A is a computer generated laser processed elliptical pattern witha single scan according to the invention.

FIG. 5B is a computer generated laser processed elliptical pattern usingthe same impact frequency matrix as in FIG. 5A with two laser scansaccording to the invention.

FIGS. 6A and 6B show computer simulated elliptical patterns with theimpact frequency matrix of different roll-off rates in accordance withthe invention.

FIG. 7A shows a computer simulated laser processed worn pattern fordenim jeans.

FIG. 7B is a density matrix indicating the right-hand-side portion ofthe worn pattern of FIG. 7A.

FIG. 8A shows another computer simulated laser processed worn patternfor denim jeans.

FIG. 8B is a density matrix indicating the right-hand-side portion ofthe worn pattern of FIG. 8A.

FIGS. 9A-9D are schematics showing different exemplary laser scanningtraces in accordance with the invention.

FIGS. 10A-10C are schematics illustrating three examples of laserprecessing system for a garment production line.

FIG. 11 shows a laser processing system with a rotating garment carouseland multiple lasers.

FIG. 12 is a block diagram further showing components of the controlcomputer.

FIG. 13A is a flowchart for one exemplary mode operation using aninitial patten density matrix.

FIG. 13B shows a probability density matrix based on the pattern densitymatrix of Table 1.

FIGS. 13C and 13D are the impact frequency matrices based on the patterndensity matrix of Table 1 with a single pass and a double pass,respectively.

FIG. 14 is a flowchart showing a user interface process based on FIG.13A.

FIG. 15 is a block diagram showing a graphic user interface based onFIG. 13A.

FIG. 16 is a flowchart for one exemplary mode operation using an initialprobability density matrix.

FIG. 17 is a flowchart showing a user interface process based on FIG.16.

FIG. 18 is a block diagram showing a graphic user interface based onFIG. 16.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a block diagram of a laser processing system for treating asurface. Solid lines with an arrow represent laser beams and dashedlines represent electrical control signals. A laser 110 of any type,including but not limited to, a gas laser and a solid-state laser incontinuous-wave ("CW") or pulsed operation mode, produces a laser beam114. A CO₂ laser may be preferred for processing many materials. Theoutput power of the beam 114 is controlled by a laser power control unit112. A beam steering and scanning device 120 is positioned relative tothe laser 110 and is operable to guide the laser beam to any location ona workpiece surface held by a support stage 140. Focusing optics 130 islocated at a desired distance from the support stage 140 relative to thebeam steering and scanning device 120. Alternatively, the workpiececould be moved relative to the beam.

A control computer 150 is used to control the operation of the laser 110including the output power, the steering and scanning of the laser beam,and the beam spot size on the support stage by changing the distancebetween the focusing optics 130 and the support stage 140. The controlof the output power of the laser 110 includes turning on/off the laserbeam, changing the output level, or other controls. Such a control canbe done either by directly controlling the laser itself or by modulatingthe output beam with a electrically-driven beam shutter and beamattenuator. Many aspects of these components are described in theabove-referenced copending application "LASER METHOD OF SCRIBINGGRAPHICS" but these alternatively can be controlled using the techniquesdisclosed in U.S. Pat. No. 5,567,207 to Lockman et al., "Method formarking and fading textiles with lasers", which is incorporated hereinby reference.

The beam steering and scanning device 120 can either direct the beam toany desired location on the support stage 140 or scan the beam over thesupport stage with a certain spatial sequence at a desired speed. Thus,the system 100 in general can be used for scribing a pattern on asurface and treating a surface to achieve a certain appearance orachieving a combination of the both.

One parameter for measuring the degree of laser interaction with asurface is the energy density per unit time ("EDPUT") as definedpreviously and as described in the above-referenced patent application,"LASER METHOD OF SCRIBING GRAPHICS". The EDPUT at the support stage canbe determined by at least one of the following: the laser power control112, the beam steering and scanning device 120 for the projection speedof the beam on the support stage 140, or the focusing optics 130 whichchanges the beam spot size. Therefore, a desired EDPUT distribution witha certain spatial profile can be achieved. This results in eitherscribing a graphic on a workpiece or producing a certain surfaceappearance. The computer 150 may have a plurality of programs forcontrolling the system 100 to achieve these functions, which will bedescribed in detail.

A variety of materials can be processed with the system 100, includingbut not limited to, fabrics, leathers, vinyls, rubber, wood, metals,plastics, ceramics, glass, and other materials. These materials can beused to make different goods. Some common examples include clothing,linens, footwear, belts, purses and wallets, luggage, vehicle interiors,furniture coverings, and wall coverings.

FIG. 2 shows an exemplary implementation 200 of the system 100. A laser210, which can be various lasers including CO₂ laser or a YAG laser,produces different power outputs. An electrically controlled beamshutter (not shown) is included in the laser 210 to turn the beam on andoff as desired. A CW CO₂ laser, "Stylus", manufactured by Excel/ControlLaser (Orlando, Fla.) may be used as the laser 210.

The laser 210 generates a laser beam 214 in the direction of a computercontrolled beam steering and scanning device having a first mirror 222and a second mirror 226. The mirror 226 is mounted on a firstgalvanometer 220 so that the mirror 226 can be rotated to move the beamin a x-axis on the support stage 140. A second galvanometer 224 is usedto control the mirror 226 so that the mirror 226 can move the beam onthe support stage 140 along a y-axis. Therefore, galvo mirrors 222 and226 can be controlled to scan the laser beam on the support stage togenerate almost any trace and geometric shapes as desired. Agalvanometer driver 260 receives commands including numerical controlcommands from the computer 150 and respectively controls the movement ofeach galvo mirror.

The laser beam 214 is deflected first by the x-axis mirror 222 andsubsequently by the y-axis mirror 226 to direct the beam through afocusing lens 230. The lens 230 is preferably a multi-element,flat-field, focusing lens assembly, which is capable of opticallymaintaining the focused spot on a flat plane as the laser beam movesacross the material. A movable stage (not shown) may be used to hold thelens 230 so that the distance between the lens 230 and the support stage140 can be changed to alter the beam spot size. Alternatively, thesupport stage may be moved relative to the lens 230.

The support stage 140 has a working surface which can be almost anysubstrate including a table, or even a gaseous fluidized bed. Aworkpiece is placed on the working surface. Usually the laser beam isdirected generally perpendicular to the surface of the support stage140, but it may be desirable to guide the beam to the surface with anangle to achieve certain effects. For example, the incident angle mayrange between about 45° and about 135°.

The computer 150 may include a designated computer such as a workstationcomputer (not shown) to facilitate the formation of the desired graphicor a control matrix. For example, a graphic can be scanned into theworkstation computer and converted into the proper format. This mayexpedite the processing speed. The computer 150 then controls the galvomirrors to impart the desired pattern to a material at the appropriateEDPUT.

The system 200 may also include a gas tank 270 to inject a gas such asan inert gas into the working zone over the support stage 140. Theamount of gas can be controlled by the computer 150. This use of aninert gas may reduce the tendency for complete carbonization,burn-through and/or melting. This technique can also produce new effectsin graphics. In general, any gas can be used in the working zone tocreate a new effect. The gas tank 270 can also be used to inject agaseous dye to add coloring on the workpiece.

The above disclosed laser systems can be used to impart graphics and/orproduce certain surface appearance on a surface of a variety of goodsand products. In particular, the systems can be used to treat fabrics tohave the worn appearance produced by the conventional sandblastingprocess. The present invention has a number of advantages over theconventional sandblast process. For example, the overall cost for thesystem hardware and operation maintenance is less expensive. The healthhazards and environmental problems of the sandblasting process areessentially eliminated. The present invention can better preserve thedurability of the treated materials than the sandblasting process. Theproduct yield of the system of the invention is higher than that of thesandblasting process due to the accuracy and repeatability of the laserprocessing. In addition, the present invention not only can generate thesandblasted look on denim but also can impart the sandblasted look onkhaki and other materials. Furthermore, precision control of the laserbeam allows the system of the invention to better control how a selectedarea will be treated while the sandblasting process simply cannot give auser much control. Yet another advantage of the invention is that lasersurface treatment for a desired appearance can be easily combined withscribing complex and intricate graphics in the treated area with thesame processing system without relying on additional devices.

A first embodiment of the invention uses the computer 150 of thepreferred system 100 in FIG. 1 to produce a probability density matrixwhich is in turn used to create a impact frequency matrix. The impactfrequency matrix is used to control the laser in producing a desiredtwo-dimensional spatial profile or pattern. A selected area to betreated on a fabric or clothing is divided into a matrix of pixels. Theimpact frequency matrix indicates the number of times each individualpixel is "hit" by the laser beam.

The computer 150 uses the impact frequency matrix to generate a set ofcontrol codes for controlling the laser power control 112 and the beamsteering and scanning device 120. The power control 112 keeps the laserbeam 114 "on" as the beam scans locations on a fabric corresponding topixels with positive impact frequencies and turns the laser beam "off"as the laser scans locations with zero impact frequencies.

Thus the laser beam 114 is turned on and off as it scans through atreated area of a desired geometric shape on a fabric. Multiple laserscans are needed at the locations that are to be hit by the beam morethan once. Areas of a fabric having locations that are hit morefrequently by the laser beam have a high degree of worn appearance.Conversely, the areas having locations that are hit by the laser beamless frequently will have a lesser degree of worn appearance. The finaleffect of the scan is equivalent to shining many laser beamssimultaneously on the fabric with a random distribution similar to theblasting of sand particles. For this reason, this laser surfacetreatment may be referred as a "laser blast" process which is analogousto the "sandblast".

The probability density matrix assigns a probability density to eachpixel. This assignment of probabilities may be done mathematically forany number of regular geometric shapes, e.g., ellipses, rectangles, etc.Alternatively, the assignment of probabilities may be set manually andstored in a data file. Thus, a probability density matrix for a selectedgeometric pattern is predictable and definite. If the probabilitydensity matrix is directly used to generate control codes of theprocessing laser, the resultant pattern will have a predictable anddefinite appearance or a "contrived" look. This cannot produce therandom feature of a sandblast pattern.

The random aspect of the sandblast pattern is preferably accomplished bythe means of impact frequency matrix. The impact frequency matrix isbased on the probability density matrix in the sense that the spatialdistribution of the probability density remains the same in the impactfrequency matrix. However, the impact frequency at each location is alsodetermined by a random number produced by a pseudo-random numbergenerated with a computer (e.g., the control computer 150 in FIG. 1).This aspect of the invention enables the impact frequency matrix tosimulate the random features of a sandblast pattern. Thecomputer-generated random numbers are based on an initial random numberseed. Using different initial random number seeds can result indifferent series of random numbers and thereby further enhances thesimulated random look. Many different patterns can be produced with eachpattern having a different choice of the initial random number seed.

Assume for the moment that the value of the probability density liesbetween 0 and 1 for each pixel. This process sets the likelihood of animpact for that pixel equal to the probability density. For example, ifa pixel has a probability density of 0.6, it has a 60% chance ofreceiving an impact of the laser beam and a 40% chance of not receivingan impact.

Probability densities greater than one are also contemplated. Ingeneral, the integer portion of the probability density for a pixelindicates the minimum value of the impact frequency for that pixel. Forexample, a probability density of 2.4 for a pixel indicates that thepixel has a 40% chance of receiving three impacts by the laser beam anda 60% chance of receiving two impacts.

According to the invention, the above technique can be extended topermit multiple passes in generating the impact frequency matrix. Inthis extension, the impact frequency matrix is generated cumulatively bytwo or more applications of the process described above using the sameor different probability density matrices.

One advantage of this process is that it simulates the random nature ofthe impact of the abrasive particles impinging upon the fabric in asandblasting process. This at least in part contributes to the muchimproved look by using the system of the invention over the effects byother laser methods previously disclosed.

FIG. 3 is a flowchart which shows a process of producing a desiredsandblasted pattern on a fabric. First, at step 310, a sample of anactual sandblasted material is obtained. The surface appearance of thesample pattern is sampled at step 320 so that the exact locations andfrequency that the sand particles hit are determined. Next at step 330,a probability density matrix is generated based on the sampling resultsof step 320 and a random number generation. The probability densitymatrix and corresponding impact frequency matrix are generated based onpseudo-random numbers. The impact frequency matrix is subsequently usedto control the laser beam at step 340 in treating a fabric to simulatethe sandblasted appearance.

The mathematical approach to setting the values of the probabilitydensity matrix can be illustrated by an elliptical pattern as shown inFIG. 4. This is an effective way of creating an oval shaped wear patternaround the knee portion of a pair of denim jeans. An elliptical area 420may be used for simplicity. In general, any geometrical shape may beused. Thus the desired replication of a sandblast pattern is one whereinthe frequency of being hit by a laser beam is greatest in the center ofthe ellipse 320 and diminishes in a continuous but random manner whenmoving away from the center toward the boundaries. This is produced by aprobability density matrix that has the highest probability value in thecenter of the ellipse and values that decrease continuously in apredetermined manner when moving toward the boundaries.

One method to produce such a probability density matrix begins with theassignment of the X and Y dimensions of the ellipse as indicated in FIG.4, the probability density at the center O of the ellipse 420 isrepresented by a and the probability density at the boundary isrepresented by b which is set to be a constant at any point on theboundary in this example. Then the probability density of a pixel, suchas indicated by point D can be determined by the ratio, R, of thedistance from the ellipse center O to D to the distance from the centerO to a point D_(b) on the boundary at which the same vector as Dintersects with the ellipse 420: ##EQU2## The probability density forthe point D is then determined as follows:

    Probability density=a+R.sup.P (b-a)

where the exponent coefficient, p, determines the "roll-off" or the rateof fade in the worn look. For example, for p>1, the roll-off may beconsidered fast; for p=1, the roll-off is moderate; and for p<1, theroll-off is slow.

FIG. 5A shows a computer generated laser blast pattern of an ellipsecreated by setting the center probability density a=0.9, the boundaryprobability density b=0.1, and the roll-off coefficient p=1, for asingle pass process. FIG. 5B shows a pattern with a, b and p set as inFIG. 5A but using a two-pass process.

FIGS. 6A and 6B show computer generated laser blasted patterns of anellipse with a maximum probability density at the center of 3.2 and aprobability density of 0 at the boundary. FIG. 6A is generated by aroll-off coefficient p=2 and FIG. 6B is generated by a roll-offcoefficient p=0.5. The significance of the roll-off is clearly shown bythe difference in outer edge distributions. Thus, the roll-off can beused to precisely control the feathering effect.

According to the invention, more complex patterns may be formed bymanually setting the values of the probability density matrix andstoring them in a data file. FIG. 7A shows a computer generated patternhaving an upper portion 710 and a lower portion 720. The upper portion710 may be used for the worn look on the lap portion of denim jeans andthe lower portion 720 may be used for the worn look in the knee area.This is one of the popular worn looks on many jeans.

FIG. 7B shows the probability density matrix in a tabular form for thelaser blasted pattern of FIG. 7A. The highest probability density is2.0. Notice that FIG. 7B only shows the probability density matrix forthe right-hand-side portion of the laser blasted pattern. The laserblasted pattern of FIG. 7A is symmetric about the line 7C--7C.

Another laser blasted pattern generated in accordance with the inventionis shown in FIG. 8A. The respective probability density matrix for theright-hand-side portion is listed in a tabular form in FIG. 8B.

The spatial orientation of the pattern on the fabric may be adjusted bysetting various operating parameters of the laser through eitherhardware or software implementation. For example, the density of thepixels and the angle of the scan may be set in such a manner.

According to a second embodiment, the impact frequency matrix may beimplemented by keeping the laser beam on at the locations that havepositive impact frequencies and adjusting operating parameters toincrease EDPUT in accordance with the impact frequency, i.e., locationswith higher impact frequencies are given higher values of EDPUT.Referring to FIG. 1, EDPUT can be adjusted by changing combinations ofthe following: the output power level with the power control 112, thescan speed by the beam scanning device 120, the relative distancebetween the focusing lens 130 and the support stage 140. The EDPUTvalues used in this embodiment are preferably within a range determinedfor each material. If the received EDPUT exceeds a maximum limit of therange, the surface may be burned or carbonized. Conversely, the effectof the laser processing may become imperceivable if the received EDPUTis smaller than a minimum limit of the range.

Therefore, one way to change the EDPUT based on the impact frequencymatrix is to correlate the EDPUT of the laser system with the impactfrequency in a linear or nonlinear relation. The EDPUT value of thelaser beam may be set to the maximum value in the allowed EDPUT rangefor that material for areas assigned with the highest impact frequenciesand to the minimum EDPUT value for areas assigned with the lowest impactfrequencies. For example, if the center of the ellipse 420 has aprobability of 1 assigned by the probability matrix, the correspondingimpact frequency matrix can be used to the EDPUT value of the laser beamat the center to the maximum EDPUT in the allowed EDPUT range for thatmaterial. At the boundary of the ellipse 420, the probability is 0 andhence the minimum EDPUT value is assigned according to the correspondingimpact frequency matrix. Other ways of correlating the impact frequencymatrix and the EDPUT values of the laser system may also be used inaccordance with the invention.

Test results demonstrated the possibility of nearly exactly simulatingthe worn look achieved from the sandblast process. The results wereparticularly encouraging because, to the best knowledge of theinventors, never before has there been a process that can achieve such alook other than the sandblast process.

One aspect of the impact frequency matrix in accordance with theinvention is its scalability. An impact frequency matrix of a patterncan be scalable with the dimension of the pattern. This scalingtechnique may be used to reduce the processing cycle time of a largepattern. For example, the cycle time to process a typical 21-inch ovalsection from the upper thigh to below the knee on a pair of denim jeanswas about at least 6 minutes for a set of operating parameters. Thecycle time may be, however, reduced by the following scaling process.

First, an impact frequency matrix is generated for a patternproportionally smaller than the desired size by a predetermined factor(e.g., a factor of 2). This is configured in a scanning control programin the control computer 150 of the system 100 of FIG. 1. For a givenareal density of scanning lines, the processing cycle time of thesmaller section is shorter than that of the desired larger section withthe same pattern.

Secondly, the scanning control program is set to change a size commandto increase the size of the image to the desired size that has beenreduced in the first step. This size command may include a heightcommand for changing the height. For example, if the pattern size usedin the first step was 1/2 of the original size, then the height commandin the laser file would be set to 2, i.e., twice as large. Thiseffectively scales an impact frequency matrix for the smaller section toprocess a larger section of the same pattern. The size command isconverted as laser control codes which control a processing laser beamto move at a prescribed distance on a workpiece according to positionsof matrix elements in the impact frequency matrix.

Next, the EDPUT is adjusted (e.g., increased) so that a high scanningspeed setting can be used to further reduce the cycle time for thedesired finishing quality.

The effect of the above scaling technique is to make the laser traversethe pattern section at the same number of scanning passes as in the casefor a pattern of a smaller (e.g., half) of the size while still keepingthe laser scans relatively congruent. An optional step of adjusting thebeam spot size may be performed after the resizing step of the scanningcontrol program, in which the spot size of the laser beam 114 isincreased to a predetermined diameter by adjusting the relative distancebetween the focusing optics 130 and the support stage 140. The amount ofincrease in the beam size usually has a relation with the size reductionfactor used in the first step. For denim and some other fabrics, thisoptional step may not be necessary because of the fabric tolerance ofthe denim.

A significant reduction in the processing cycle time can be achieved byoptimizing the operating parameters, including but not limited to, thescaling factor, the amount of increase in the beam size, the laserscanning speed, and the power of the laser. In processing an 21-inchoval, for example, the processing cycle time can be reduced by six foldsfrom about 6 minutes to about 1 minute with a scaling factor of 2.

Another aspect of the impact frequency matrix technique is that theimpact frequency matrix can be easily configured to generate a varietyof different surface looks including different degrees of wearing in thesandblasted worn look. For example, an impact frequency matrix can begenerated to produce a variety of pixelated looks and looks as if ashotgun pellets or other media were blasted onto the fabric. This can beaccomplished by merely changing the probability densities within aboundary of a desired pattern. For example, probability densities at thecenter and boundary of the previously-described elliptical pattern inFIG. 4 can be changed for different looks. In addition, various graphicscan be superimposed in a laser blasted section using the same lasersystem. A graphic may be scribed onto a selected area of a fabric firstand then the laser blasted process is performed to achieve a desiredworn effect on the scribed graphic.

Few surface processing techniques, including the sandblasting processand the previously disclosed laser techniques, are capable of providingthe flexibility, diversity, and the precise control of the preferredmatrix technique of the present invention.

According to the invention, multiple laser scanning passes are performedin treating a selected section of a surface. In general, any beamscanning scheme may be used in accordance with the invention. Forexample, a commonly used line scanning scheme may be used to scan asurface in a line-by-line manner with each scanning line being asubstantially straight line. FIGS. 9A and 9B show two examples ofscanning in straight lines. The inventors discovered that non-straightscanning lines may also be used to achieve certain surface appearancethat may not be possible with straight scanning lines. In particular,scanning in non-straight lines may be used to enhance the featheringeffect on a fabric. Referring to FIG. 1, the beam steering and scanningdevice 120 and/or the focusing optics 130 may be controlled with thecontrol computer 150 so that the trace of the scanning beam on a surfaceforms a certain waveform pattern. FIG. 9C shows a sine or cosine typescanning line. FIG. 9D shows "wobbling" scanning lines. Two adjacentwobbling lines may or may not overlap with each other. The wobblingscanning lines can be used in the scaling technique to compensate forthe increased scanning spacing due to the increase in the size of anarea to be processed.

FIGS. 1 and 2 generally show laser processing systems for scribinggraphics and treating surface on a workpiece. These systems can be usedfor processing denim jeans or other garments. FIGS. 10A-10C illustratethree examples of a laser processing system for denim jeans. A motorizedcarrier 1010 (e.g., an assembly line) provides an automated way forfeeding denim jeans one by one to a processing location wherein thelaser system is located. An autosizer 1020 having automatic sizingsensors to detect the actual size of the garment so that a properlocation can be determined to impart either a graphic or a worn look. InFIG. 10A, a single laser beam produced by a laser 1030 is used toprocess one section at a time. Multiple laser beams can be used tosimultaneously processing multiple sections on a pair of denim jeans toincrease the processing speed of the system. For example, FIGS. 10B and10C show that two lasers 1030 and 1040 are used produce two beams forsimultaneously processing two different sections on pair of jeans. Thelasers can be positioned on top of a table with a laser beam impingingupon the fabric approximately in a vertical direction or the lasers canbe positioned so that a laser beam impinges upon the fabricapproximately in a horizontal direction.

FIG. 11 shows another laser processing system in accordance with theinvention. A motorized rotating carousel 1110 is used so that the jeansdraped over a form can be automatically fed to a processing location.One or more laser beams can be used to simultaneously process one ormore sections on a pair of jeans. The example of FIG. 11 shows that thefront legs and back panels are being processed as the rotating carousel1110 indexes the garment for subsequent processing.

Another aspect of the invention is that the laser processing process maybe used either after the garments are sewn and washed, or before theyare sewn and washed.

FIG. 12 further shows some components that can be included in thecontrol computer 150 of FIG. 1. A central processing unit ("CPU") 151 isthe engine of the computer 150 which includes a microprocessor. A memoryunit 152 is used to store data and instructions. For example, the datamay include the geometrical shape of a pattern, a pattern densitymatrix, the probability density matrix, the impact frequency matrix, andlaser control codes. The instructions may include software packages for,e.g., generating the pseudo-random numbers, producing probabilitydensity and impact frequency matrices, controlling display contents,managing data, and controlling various components in the laserprocessing system.

A user input device 153 receives and transmits a user's instructions orentered data to the CPU 151. A cursor-pointing device (e.g., a mouse), acomputer keyboard, or a touch-screen input device may be used alone orin a combination to serve as the user input device 153.

A display 154 may be any device capable of displaying text and graphics,such as a CRT monitor, a LCD display, or a video projection device.

An input/output interface 155 indicates either a stand-alone interfaceor a portion of an integrated interface that connects to othercomponents of the laser processing system. For example, FIG. 1 showsthat the laser power control 112, the beam steering and scanning device120, and focusing optics 130 may be connected to and communicated withthe CPU 151 through the interface 155.

A user control interface is implemented in the system. The interfaceincludes the user input device 153 and the display 154 which aresupported by the CPU 151, the memory unit 152 and other components ofthe control computer 150. This feature allows a user to simulate asandblast pattern produced with an impact frequency matrix by a graphicrepresentation of the pattern on the display 154. Such a visualrepresentation of the pattern may be used to determine the appearance ofa pattern or to compare the effects of different impact frequencymatrices for the same geometrical pattern, prior to actually marking thepattern onto a surface by the laser.

For example, the geometry of a pattern can be any shape and can beconveniently and quickly generated by a software at any time accordingto a user's desire. The characteristics of the probability densitymatrix, such as roll-off coefficient for feathering effects and themaximum/minimum probability densities, may be changed during thesimulation stage until a desired result is achieved. The initial randomnumber seed may also be altered to obtain different random numbers informing the impact frequency matrix.

All these and other pattern manipulations can be done through the usercontrol interface of the control computer. Advantages of this aspect ofthe invention include flexibility, reduced cost and time of design.

A processing process different to the process shown by the flowchart 300may be implemented by using the user control interface. One embodimentis shown in FIG. 13A.

Initial geometry (e.g., shape and dimension) and the "blasting" densitydistribution are selected to form a pattern density matrix. Similar tothe probability density matrix, each element in the pattern densitymatrix includes information of both the geometrical shape and thedensity. Preferably, the pattern density matrix is small, for example,limited up to about a few hundred elements in each dimension. The shapemay be any shape selected by the user or to meet a need in a specificapplication. In particular, any irregular pattern may be implemented ina pattern density matrix.

The geometrical features of a pattern represented by a pattern densitymatrix may be created in a systematic manner using mathematical formulasor equations. This systematic approach may be advantageous in certainshapes and can substantially eliminate the size limitation of a patterndensity matrix since the pattern matrix may be generated by using acomputer. However, for certain irregular patterns and particularly someunusual artistic geometric patterns, implementation of the abovesystematic method may be time consuming since complex mathematicalderivation or calculations may be necessary to derive one or moreformulas and equations to represent the irregularities of the shape.Hence, a small size pattern density matrix may be created manually bytyping in the desired matrix elements through, for example, the computerkeyboard, or by converting a graphic pattern in digital form intodesired matrix elements.

The pattern density matrix may be edited at any time by the user. Inaddition, the pattern density matrix may be in numerical tabular form asa conventional matrix or in a graphical form. The pattern density matrixcan be saved in the memory unit 152 for further processing. Thiscompletes the step 1310.

In step 1320, scale factors are first determined for expanding thepattern density matrix into a probability density matrix at a desiredsize. One scale factor is sufficient if the scaling is only performed inone direction. Two more scaling factors may be needed for more complexscaling operations in multiple directions. A linear interpolation may beimplemented in forming a probability density matrix from a patterndensity matrix in order to preserve the relative density distribution ofthe original pattern density matrix. This linear interpolation is twodimensional since it is performed in the same plane. In many practicalcases, a linear interpolation in each of two orthogonal directions maydesirable.

Next in step 1330, an initial random number seed is selected and theimpact frequency matrix is formed by correlating the probability densitymatrix with the random numbers produced by a pseudo-random numbergeneration based on the seed.

In step 1340, a graphic representation of the impact frequency matrix isgenerated. This may be done by using a graphic program. The graphic isdisplaced on the display 154 to show the user what would be theappearance of a treated surface if the impact frequency matrix isactually used to process a surface with the laser processing system.

If the user decides the appearance is satisfactory, the impact matrix isthen used to generate laser control codes for a subsequent surfacetreatment.

If, however, the user decides the surface appearance is notsatisfactory, the impact frequency matrix may be changed by adjusting atleast one of the following: the pattern density matrix by following theloop 1342, the probability density matrix by following the loop 1344, orthe initial random number seed by following the loop 1346. The aboveprocess may be iterated multiple times until a desired graphicrepresentation is achieved with the impact frequency matrix.

Table 1 shows an example of a 5×5 pattern density matrix. The values ofthe matrix elements dictate both the density distribution and thegeometrical shape. In this example, the pattern density matrix of Table1 shows a diamond-like shape and a maximum density value at the centerand a density distribution that decreases from the center to theperipheral.

                  TABLE 1                                                         ______________________________________                                        Pattern Density Matrix                                                        ______________________________________                                        0           0     0.4         0   0                                             0 0.4 0.8 0.4 0                                                                 0.2 0.6 1.0 0.6   0.2                                                       0 0.4 0.4 0.4 0                                                               0 0   0.4 0   0                                                             ______________________________________                                    

A 2D linear interpolation can be performed on the pattern density matrixshown in Table 1 to produce a respective probability density matrix. Forexample, two scaling factors, 2 and 3, can be selected for x and ydirections, respectively. Thus, the probability density matrix has 10columns and 15 rows (i.e., a 15×10 matrix). FIG. 13B shows theprobability density matrix.

Next, a 15×10 array of pseudo-random numbers produced from a selectedseed is used to correlate with the probability density matrix. Thisgenerates a impact frequency matrix as shown by FIG. 13C for a singlepass process. For a two-pass process (i.e., corresponding to a maximumdensity value of 2), the impact frequency matrix is shown in FIG. 13D.

The flowchart 1300 reflects the execution steps of a software thatcontrols the user control interface. This process may take a differentform to the user at the user control interface in order to be userfriendly and convenient. For example, the steps 1320 and 1330 and theassociated with the feedback loops 1344 and 1346 may appear as asingle-step process of producing the impact frequency matrix to theuser. Therefore, one embodiment of the user interface flow can look likeFIG. 14.

Initially, a user is given the option to either retrieve a pre-storedpattern density matrix in the memory or input a new one (step 1410). Anoption may be implemented to allow the user to view the density matrixin either tabular mode or graphical mode. At step 1420, a user entersall parameters for the probability density matrix and impact frequencymatrix. The user then proceeds to generate the impact frequency matrixat step 1430. Subsequently, the graphic rendition of the impact matrixis displayed on the screen. At this point, the user may choose one ofthe three choices: go ahead to generate the laser codes (step 1450),reset the screen parameters to generate a new impact frequency matrix(loop 1444), or use another pattern density matrix to restart theprocess. Notice that the underlying execution of step 1320 (generatingprobability density matrix) in the actual software process is invisibleto the user in the user interface.

An on-screen graphic user interface (GUI) may be implemented based onthe flowchart 1400. An example is shown in FIG. 15.

For applications with geometrical shapes that may be generated withmathematical formulas or equations, the steps related to a patterndensity matrix can be eliminated since a probability density matrix canbe easily created by the control computer. Elliptical shape patternsmarked on jeans are examples of this type of applications. FIG. 16 showsan embodiment of the control software for the user control interface.FIG. 17 shows an embodiment of the user interface flowchart. FIG. 18shows an example of the GUI based on the flowchart of FIG. 17.

The above-described user control interface may also be used in scribingpatterns on a surface. Thus, a pattern may be displayed for inspectionor design purpose prior to actual processing.

Although the present invention has been described in detail withreference to the preferred embodiment, one ordinarily skilled in the artto which this invention pertains will appreciate that variousmodifications and enhancements may be predictable. For example, thesupport stage 140 in the system 100 of FIG. 1 can be movable by a motorcontrolled by the control computer 150 so that a fixed laser beam can beused for scribing graphics or creating a worn look since a fabric can bemoved relative to the laser instead.

For another example, the single output beam 114 from the laser 110 maybe divided into multiple beams and each of the multiple beams can beindependently controlled with a set of beam steering and focusingdevices. Therefore, the multiple beams from the single laser may be usedto simultaneously process different sections of a garment.

Furthermore, two independently-controlled scanning laser beams may beused simultaneously to process a same section of a garment with onescribing a graphic and another one producing a desired worn look. Thismay also increase the throughput of the system.

Yet another variation of the preferred embodiment is implementation ofmulti-pattern processing with a single execution of the controlprocesses illustrated in FIGS. 3, 13, 14, 16 and 17. Two or moreprocessing laser beams are controlled by the same impact frequencymatrix to process two or more different areas on one or more workpieces.For example, the same pattern would be created on both sides of agarment by using position offsets and angular realignments incontrolling one or two laser beams. If a single laser is used, the beamposition and direction are changed from processing one area toprocessing another area with the same impact frequency matrix. Thus, twoareas are sequentially processed. If two lasers are used, the positionoffsets and angular realignments are used to control the lasers to aimat different areas with possibly different directions. In this case, thetwo areas are processed simultaneously according to the same impactfrequency matrix.

These modifications and others are intended to be encompassed by thefollowing claims.

What is claimed is:
 1. A sandblasting simulating apparatus, comprising:alaser system, producing a laser beam which moves relative to a surfaceof a material to mark a pattern on said material according to an appliedcommand; a controller connected to said laser system and configured tocommunicate with said laser system to generate said applied commandaccording to information indicative of said pattern, said informationincluding a pseudo-random characteristic which simulates a sandblastedeffect; and a user control interface which includes a user input deviceand a display, said user control interface connected to said controllerand configured to produce a graphic representation of said pattern basedon said information on said display prior to actually processing saidmaterial with said laser system and to allow for modification of saidlaser impact frequency information.
 2. An apparatus as in claim 1,wherein said information is in the form of a laser impact frequencymatrix in which values and positions of matrix elements indicategeometry and appearance of said pattern and said impact frequency matrixis generated by a correlation of pseudo-random numbers with aprobability density matrix indicative of processing density of lasermarking within said geometry of said pattern.
 3. An apparatus as inclaim 2, wherein said modification of said laser impact frequencyinformation is performed by changing said probability density matrix. 4.An apparatus as in claim 2, wherein said modification of said laserimpact frequency information is performed by changing said pseudo-randomnumbers.
 5. An apparatus as in claim 2, wherein said user controlinterface is configured to effect a user graphic interface displayed onsaid display, said user graphic interface including a display window fordisplaying graphics and texts and a command window having a plurality ofuser control buttons.
 6. An apparatus as in claim 5, wherein said usercontrol buttons include a first control button for receiving or creatingsaid probability density matrix, a second control button for settingscreen parameters for editing said probability density matrix and impactfrequency matrix, a third control button for executing a display of asimulated pattern, a fourth control button for generating laser controlcodes, and a fifth control button for sending said laser control codesto said laser system.
 7. An apparatus as in claim 3, wherein saidprobability density matrix is generated by a pattern density matrix byperforming a linear interpolation using user-selected scalingparameters.
 8. An apparatus as in claim 7, wherein said controllercomprises:means for determining said pattern density matrix indicativeof said pattern; means for generating said probability density matrix inresponse to user's parameters based on said pattern density matrix;means for generating said impact frequency matrix based on auser-selected random seed number for generating said pseudo-randomnumbers; means for producing a graphic representation of said patternaccording to said impact frequency in response to a user command; andmeans for generating said laser control codes using said impactfrequency matrix.
 9. An apparatus as in claim 2, wherein said controllerincludes:means for generating said probability density matrix inresponse to user's parameters based on said initial pattern densitymatrix; means for generating said impact frequency matrix based on auser-selected random seed number for generating said pseudo-randomnumbers; means for producing a graphic representation of saiduser-defined pattern according to said impact frequency in response to auser command; and means for generating laser control codes using saidimpact frequency matrix.
 10. A method of simulating a sandblastingpattern using laser processing, comprising:forming a probability densitymatrix indicative of geometry and appearance of the sandblastingpattern; correlating a set of pseudo-random numbers with saidprobability density matrix to generate an impact frequency matrix; andgenerating laser control codes based on said impact frequency matrix.11. A method as in claim 10, further comprising:producing a graphicrepresentation of said sandblasting pattern according to said impactfrequency matrix; and modifying said impact frequency matrix when saidgraphic representation deviates from said appearance of said pattern.12. A method as in claim 11, wherein said modifying is achieved bychanging said pseudo-random numbers.
 13. A method as in claim 11,wherein said modifying is achieved by changing said probability densitymatrix.
 14. A method as in claim 10, further comprising controlling afirst laser to mark said pattern on a material by using said lasercontrol codes.
 15. A method as in claim 14, further comprisingsimultaneously controlling a second laser with said laser control codesto mark said material at another location.
 16. A computer program,residing on a computer-readable medium, comprising instructions forcausing a computer to:form a probability density matrix indicative ofgeometry and appearance of a sandblasting pattern; correlate a set ofpseudo-random numbers with said probability density matrix to generatean impact frequency matrix; and generate laser control codes based onsaid impact frequency matrix.
 17. A computer program as in claim 16,further comprising instructions for causing the computer to:produce agraphic representation of said sandblasting pattern according to saidimpact frequency matrix; and modify said impact frequency matrix whensaid graphic representation deviates from said appearance of saidpattern.
 18. A computer program as in claim 17, wherein said impactfrequency matrix is modified by changing said pseudo-random numbers orby changing said probability density matrix.
 19. A computer program asin claim 16, further comprising instructions for causing the computer tocontrol a first laser to mark said pattern on a material by using saidlaser control codes.
 20. A computer program as in claim 19, furthercomprising instructions for causing the computer to simultaneouslycontrol a second laser with said laser control codes to mark saidmaterial at another location.